A novel reactor, combining the advantages of the MODAR reactor, horizontal stirred reactor, dynamic gas seal wall reactor, and cool wall reactor, was designed and manufactured to overcome the problems encountered in continuous supercritical water oxidation of real waste, especially in semi-solid state. It is a Y-shaped reactor consisting of an inclined reaction section on the left and a vertical separation section on the right. Nine experiments were carried out to test the performance of the reactor using municipal sewage sludge (MSS), with 12% dry solid (DS) content, as a representative sample of real waste. The results suggest that MSS, without preheating, can be safely and efficiently treated by adding 12.5% isopropyl alcohol (IPA) and pure supercritical water, the volume of which is at least 2.5 times that of the MSS. The organic carbon removal efficiency is up to 99.94%. Inorganic solid particles from the MSS are continually pushed forward in the inclined reaction section, and are completely separated and stored at the bottom of the vertical separation section. Clean effluents, comprising water and gases as the main products, are released from the top outlet. The flow regime in the inclined reaction section can be considered to be plug flow. Counter-current flow was not observed during the tests. The excellent in situ solid separation efficiency suggests that this reactor has potential for application in various hydrothermal processes that involve high content of inorganic solid particles.